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Introduction to Programming with Java

Introduction to Programming with Java. AP Computer Science ASFA. What is an Object?. A person, place, or thing That knows something about itself Has data (attributes, fields) A cashier has a id, name, and a password And can do something Has operations (methods)

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Introduction to Programming with Java

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  1. Introduction to Programmingwith Java AP Computer Science ASFA

  2. What is an Object? • A person, place, or thing • That knows something about itself • Has data (attributes, fields) • A cashier has a id, name, and a password • And can do something • Has operations (methods) • A cashier can total the items, take payment, make change Intro-OO

  3. What is a Class? • The type of an object • The way we classify an object • “The Idiot” by Dostoevsky is a book • “War and Peace” by Tolstoy is a book • Caitlin is a cashier • Kheri is a cashier • Grouping of objects with the same data and operations Intro-OO

  4. We will use the Java language to model our objects on the computer • Cashier has attributes: • Name • Id number • Cashier can perform: • Make change • Calculate order total

  5. This would be modeled in Java as a Cashier class with memory set aside to store: • Name • Id number And instructions on how to perform: • Make change • Calculate order total Alexander and Jefferson are both Cashier objects Alexander has a different name and id number than Jefferson, but they both make change the same way

  6. Now Let’s Look at the Small Steps • How are we going to make this happen through a computer program?

  7. Part 1 What is a computer? What is this programming thang? What is Java?

  8. What is a Computer? • A device that performs high-speed mathematical and/or logical operations or that assembles, stores, correlates, or otherwise processes information. • The first computers were people • who did computations

  9. Why Do Computers Keep Getting Cheaper? • The number of transistors (a major component of the brain of a computer) at the same price doubles every 18 months • making computers faster, smaller, and cheaper over time • This notion is know as Moore’s Law • For Gordon Moore, a founder of Intel • This “Law” has held true for decades • And is predicted to hold true at least one more

  10. What are Computers Good At? • Doing calculations and comparisons • Producing the same answer every time • Like calculating the sum of hundreds of numbers • Storing information • They don’t forget information • Looking up information quickly • Search through a phone book to find the customer name for a phone number

  11. What is Programming? • Creating detailed instructions that a computer can execute to accomplish some task. • Like writing a recipe for your favorite dish • Or giving someone directions to your house • Or making a robot do what you want

  12. Early Programming • Early computers required the programmer to set switches and move wires • Which represented a series of 1’s and 0’s • Later computers were programmed using punched cards

  13. Language Evolution • Early languages were based on how to do instructions on each machine • 1’s and 0’s to add, subtract, read, store, etc • Assembler allowed you to write programs using names for instructions and memory • But still translated into machine language • Higher-level languages • Are compiled into machine language or virtual machine language (Java)

  14. Java • Developed at Sun in the early 1990s • Invented by James Gosling • Similar to C++ in syntax but easier to use • Less likely to crash • Automatic memory management • Cross-platform, object-oriented language • One of the fastest adopted technologies of all time • Current favorite language, for now

  15. Which Language? • All high-level languages are eventually translated into machine language • You can write the same program in any language • The computer doesn’t care what high-level language you use • The language matters to the programmer • How long does it take to write the program? • How hard is it to change the program? • How long does it take to execute?

  16. Why Don’t We Just Use English? • English is good for communication between two intelligent humans • Even then we sometimes don’t understand • Computers are very stupid • They basically know how to add, compare, store, and load • Programs are very detailed instructions • Everything must be precise and unambiguous

  17. Programming Exercise • Write down instructions for how to make a paper airplane • Have your partner read the directions and make an airplane • stop anytime anything isn’t clear and ask for clarification

  18. Summary – Part 1 • Computers perform calculations and comparisons • A program is a series of instructions to a computer • Programming has changed from moving wires to writing textual programs that can be stored and executed several times • Java is a high level popular programming language

  19. Part 2 How does the computer do it?

  20. Parts of a Computer • User Interface • monitor (screen), mouse, keyboard, printer • Brain - Central Processing Unit • can do math and logic operations • Memory - Storage • main - RAM • secondary – Disks, CD-ROMs, DVDs

  21. CPU – Brain of the Computer • Arithmetic/Logic Unit (ALU) • Does math and logic calculations on numbers in registers • Control Unit • Reads instructions from memory and decodes and executes them using the ALU 345 Add register A to register B 263 Store the value in register C into memory location 320843202 608

  22. Fetch, Decode, Execute Cycle • The control unit reads (fetches) an instruction from memory • The control unit decodes the instruction and sets up the hardware to do the instruction • like add the values in the A and B registers and put the result in the C register • The instruction is executed • The program counter is incremented to read the next instruction

  23. Processor Speed • Processors (CPUs) have a clock • Clock speed is measured in megahertz (MHz) or gigahertz (GHz) • Some instructions take just 2-3 clock cycles, some take more • When the clock speed increases the computer can execute instructions faster

  24. Memory • Computer memory is used to store data • The smallest unit of memory is a bit (Binary digIT) • A bit can be off (no voltage) or on (has voltage) which we interpret to be 0 or 1 • Memory is organized into 8 bit contiguous groups called bytes. A megabyte is 1 million bytes. A gigabyte is 1 billion bytes.

  25. Types of Memory • Registers • Very high speed temporary storage areas for use in the CPU • Used for calculations and comparisons • Cache • High speed temporary storage for use with the CPU • Main Memory – Random-access Memory (RAM) • High speed temporary storage • Contains programs and data currently being used • Often described in Megabytes (MB) • Secondary Memory - Disks • Contains programs and data not currently being used • Often described in Gigabytes (GB)

  26. Why are there so many types of memory? • The faster memory is the more it costs • So we reduce the cost by using small amounts of expensive memory (registers, cache, and RAM) and large amounts of cheaper memory (disks) • Why do we need cache? • Processors are very fast and need quick access to lots of data • Cache provides quick access to data from RAM

  27. How does Memory Represent Values? • The different patterns of the on and off bits in a byte determine the value stored • Numbers are stored using binary numbers • 101 is 1 * 20 + 0 * 21 + 1 * 22 = 1 + 4 = 5 • 1010 is 0 * 20 + 1 * 21 + 0 * 22 + 1 * 23 = 2 + 8 = 10 • Characters are internally represented as numbers • Different numbers represent different characters • There are several systems for assigning numbers to characters: • ASCII, EBCDIC, and Unicode

  28. Binary Exercise • Count as high as you can using just the fingers on one hand • You have to count up by ones • No counting by 10s • The fingers can be up or down • No in-between states • How high can you count?

  29. Binary Numbers • We usually work with decimal numbers with digits from 0 to 9 and powers of 10 7313 = (7 * 1000 + 3 * 100 + 1 * 10 + 3 * 1) Or (7 * 103 + 3 * 102 + 1 * 101 + 3 * 100) • The binary number system uses digits 0 and 1 and powers of 2 0101 = (0 * 8 + 1 * 4 + 0 * 2 + 1 * 1) Or (0 * 23 + 1 * 22 + 0 * 21 + 1 *20) = 5

  30. To add two decimal numbers you add the digits and if the total is greater than ten you carry the one into the next column To add two binary numbers 0 + 0 = 0 0 + 1 and 1 + 0 = 1 1 + 1 = 0 with a carry of 1 into the next column to the left 00 10 111 01 01 001 ---- --- ------ 01 11 1000 00111001010 01010101101 ------------------- 10001110111 Binary Addition

  31. It’s Hard to Work in Binary • Convert to Octal • Base 8 • For example: • A is 65 in decimal and 0101 in octal • What is q in octal? 0161 • Or Hexidecimal • Base 16 • For example: • A is 65 in decimal and 0x41 in hexidecimal • What is a space in hex? 0x20

  32. Decimal Number Storage • How do you think a computer stores: 3205.406? • It uses an IEEE 754 format • Converts the number into a value between 0 and 1 raised to a power of 2 • Stores 3 things • A bit for the sign • A number between 0 and 1 (the mantissa) • The power of 2 (the exponent)

  33. Encode and Decode Exercise • Use Unicode to write a secret message in decimal and then exchange it with another person • See Appendix B in the Java Concepts textbook for the decimal values for characters

  34. Encodings Make Computer Powerful • Voltages are interpreted as numbers • Numbers can be interpreted as characters • Characters can be interpreted to be part of a link to Sun’s Java Site (for example) <a href=http://java.sun.com>Sun’s Java Site </a> a 0100 0001 off on off off off off off on

  35. Summary – Part 2 • Computers are commonplace and very important to modern life • Computers are made up of parts • CPU – calculation and comparisons • Memory – temp storage • Disk – permanent storage • Monitor – Display • Keyboard and mouse – User input • All data in a computer is stored in bits • More data takes more bits • All characters can be represented as a series of 0s and 1s

  36. Introduction to Java, and DrJavapart 3

  37. Part 3 Introduction to Java, and DrJava

  38. What is DrJava? • DrJava is a free integrated development environment for doing Java programming • From Rice University • It is written in Java • It has several window panes in it • For creating programs (definitions pane) • For trying out Java code (interactions pane) • Listing of open files (files pane)

  39. Dr. Java • We will use Dr. Java to create our Java programs • But, first, we will use it to try out some mathematical operations

  40. Math Operators in Java (+ * / - %) • Addition 3 + 4 • Multiplication 3 * 4 • Division 3 / 4 • Subtraction 3 – 4 • Negation -4 • Modulo (Remainder) 10 % 2 and 11 % 2

  41. Math Operators Exercise • Open DrJava and do the following in the interactions pane • Subtract 7 from 9 • Add 7 to 3 • Divide 3 by 2 • Divide 4.6 by 2 • Multiply 5 by 10 • Find the remainder when you divide 10 by 3

  42. Why is the result of 3 / 2 = 1? • Java is a strongly typed language • Each value has a type associated with it • Tells the computer how to interpret the number • It is an integer, floating point, letter, etc • The compiler determines the type if it isn’t specified (literals) • 3 is an integer • 3.0 is a floating point number (has a fractional part) • The result of an operation is in the same type as the operands • 3 and 2 are integers so the answer is an integer 1

  43. Casting • There are other ways to solve the problem of 3 / 2 has a result of 1 • You can make one of the values floating point by adding .0 • 3.0 / 2 • 3 / 2.0 • The result type will then be floating point • Or you can cast one of the values to the primitive types: float or double • (double) 3 / 2 • 3 / (float) 2

  44. Casting Exercise • Use casting to get the values right for splitting up a bill for 3 people of 19 dollars. • Try it first by hand • Try it in DrJava without casting • Try it in DrJava with casting

  45. Java Primitive Types • Integers (numbers without fractional parts) are represented by • The types: int or short or long • 235, -2, 33992093, etc • Floating point numbers (numbers with fractional parts) are represented by • The types: double or float • 3.233038983 -423.9, etc • A single character is represented by • The type: char • ‘a’ ‘b’ ‘A’ etc • True and false values are represented by • The type: boolean • true or false

  46. Why so Many Different Types? • They take up different amounts of space • They have different precisions • Usually use int, double, and boolean • byte uses 8 bits (1 byte) 2’s compliment • short uses 16 bits (2 bytes) 2’s compliment • int uses 32 bits (4 bytes) 2’s compliment • long uses 64 bits (8 bytes) 2’s compliment • float uses 32 bits (4 bytes) IEEE 754 • double uses 64 bits (8 bytes) IEEE 754 • char uses 16 bits (2 bytes) Unicode format

  47. 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits 8 bits Sizes of Primitive Types byte short int long float double char

  48. Types Exercise • Which type(s) take up the most space? • Which type(s) take up the least space? • What type would you use for • The number of people in your family • A grade • The price of an item • The answer to do you have insurance • The number of people in the class • The number of people in your school • The number of people in your state

  49. Floating Point Numbers • Numbers with a fractional part • 6170.20389 • Stored as binary numbers in scientific notation -52.202 is -5.2202 x 101 • The sign (1 bit) • The digits in the number (mantissa) • The exponent (8 bits) • Two types • float – 6-7 significant digits accuracy • double – 14-15 significant digits accuracy

  50. Greater than > 4 > 3 is true 3 > 3 is false 3 > 4 is false Less than < 2 < 3 is true 3 < 2 is false Equal == 3 == 3 is true 3 == 4 is false Not equal != 3 != 4 is true 3 != 3 is false Greater than or equal >= 3 >= 4 is true 3 >= 3 is true 2 >= 4 is false Less than or equal <= 2 <= 3 is true 2 <= 2 is true 4 <= 2 is false Comparison (Relational) Operators

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